It is well known to form a pattern of electrically conductive wires on glass substrates in the manufacture of such devices as heated windows for automobiles, entry sensors for burglar alarm systems, heating panels, etc. Automobile rear window defoggers, for example, are made commercially by silk screening a paste containing a mixture of silver and glass particles onto the surface of a glass panel in a desired wire pattern and firing the panel to fuse the mixture to the panel. U.S. Pat. No. 3,900,634, for example, employs particles which are less than five microns in size including a mixture of glasses having different softening points. U.S. Pat. No. 3,772,075, on the other hand, silk screens glass particles onto a glass substrate, fires the particles to form a frit bonded to the substrate, deposits electroless metal atop the frit, and, thereafter deposits a layer of electrolytic metal atop the electroless deposit.
Heretofore, the narrowest wires producible commercially (i.e., on a regular production basis) by the silk screening process has been about 750 micrometers wide and the wires so produced have projected above the plane of the surface of the glass panel to which they have been attached. Wires of such width are quite visible and thus not only effect the appearance of the vehicle but must be widely spaced to avoid obscuring visibility through the window. Wide spacing of the wires results in non-uniform heating of the glass, while projection above the surface of the glass renders them more readily damagable (e.g., scratched). Damage to any wire can result in: a break in its electrical continuity; and large areas of unheated glass.
It would be highly desirable to have an improved wire-glass composite (e.g., window deicer) with ultra-thin, conductor wires spaced more closely together (i.e., for more uniform heating of the glass without obstructing vision) and to have conductor wires whose electrical continuity would not be as easily disrupted in the event the surface of the glass is scratched, or the like, during manufacture. Accordingly, it is the principal object of the present invention to provide such an improved wire-glass composite and a method of making same. These and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.